Gyula Greschik
University of Colorado Boulder
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Gyula Greschik.
Astronomical Telescopes and Instrumentation | 1998
Arthur Palisoc; Gordon Veal; Costas Cassapakis; Gyula Greschik; Martin Mikulas
An intensive investigation has been carried out to study the surface profiles obtained as a result of the large deformations of pressurized membranes. The study shows that the inflated membrane shapes may have the requisite surface accuracy for use in future large space apertures. Both analytical and experimental work have been carried out. On the analytical side, the classical work of Hencky on flat circular membranes was extended to eliminate the limitations it imposed; namely a lateral non-follower pressure with no pre-stress. The result is a computer program for the solution of the pressurized circular membrane problem. The reliability of the computer program is demonstrated via verification against FAIM, a nonlinear finite element solver developed primarily for the analysis of inflated membrane shapes. The experimental work includes observations made by Veal on the (W-shaped) deviations between the membrane deflected shape and the predicted profile. More recent measurements have been made of the deformations of pressurized flat circular and parabolic membranes using photogrammetric techniques. The surface error quantification analyses include the effect of material properties, geometric properties, loading uncertainties, and boundary conditions. These effects are very easily handled by the special FEM code FAIM which had recently been enhanced to predict the on-orbit dynamics, RF, and solar concentration characteristics of inflatable parabolic antennas/reflectors such as the IAE that flew off the space shuttle Endeavour in May 1996. The results of measurements have been compared with analyses and their ramifications on precision-shape, large-aperture parabolic space reflectors are discussed. Results show that very large space apertures with surface slope error accuracies on the order to space reflectors are discussed. Results show that very large space apertures with surface slope error accuracies on the order of 1 milliradian or less are feasible. Surface shape accuracies of less than 1 mm RMS have been attained on ground measurements.
46th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference | 2005
Frederick H. Redell; David Lichodziejewski; Justin Kleber; Gyula Greschik
L’Garde, Langley Research Center, and Georgia Technical Research Institute have accomplished much in the area of planar membrane waveguides. A waveguide offers a method of providing transmit/receive communications for spacecraft. The advantage of the planar membrane waveguide concept, in addition to its lightweight and low packaged volume, is its inherent shape. Relative to parabolic antennas, the requirement to make an accurate doubly curved surface is removed. This paper summarizes the development of a lightweight waveguide structural technology utilizing inflation-deployed sub-Tg rigidization methods to provide a complete gossamer antenna system. The purpose of this investigation was to advance the readiness level of the inflatable planar support structure. This work summarizes the design, analysis, testing, and fabrication of an inflation-deployed rigidized support structure for the waveguide array thus advancing the gossamer antenna system. Work includes breadboard testing of component level struts, stiffness measurements of struts, and deployment testing of a prototype system. Testing included shape and dimensional performance measurements under ambient conditions. Photogrammetry results show a planar surface accuracy of 0.84 mm RMS for the sensing area of the waveguide and 1.50 mm RMS for the structure. The result is an advanced system ready to move to the next phase. The new structural technology will lend itself to a wide range of applications.
46th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference | 2005
Frederick H. Redell; Justin Kleber; David Lichodziejewski; Gyula Greschik
This paper summarizes the development of L’Garde’s Long Lived Solar Concentrator technology which utilizes material rigidization methods to provide a long lasting reflector shape without requiring continuous inflation. Material studies were conducted and testing completed on 1 m reflectors to down select work-hardening of an aluminum/plastic laminate as the rigidization method of choice over cold rigidization of a Kevlar®/thermoplasticelastomer composite. The results of the surface measurements are summarized showing slope errors as low as 12 milliradian and a focal dot with a radius as small as 37 mm. Two 3m reflectors were constructed with one tested by photogrammetry and the results compiled while the second is packaged for future testing at NASA Glenn’s Tank 6 Solar Simulator facility. Significant sciential data were collected through testing which showed that even when subjected to 1 g earth loading conditions, the shape of the reflector could be maintained allowing for future ground testing of the concept. The result is an advanced concept poised for continued development. The results of a system study using this technology are summarized and give guidance to properly sizing and positioning the reflector system on a spacecraft. The heart of this technology advancement resides in its mission enabling capability. This technology advancement diminishes two hurdles for large power concentration. First, rigid mirror reflectors require large spaces to stow thereby limiting the aperture size of the concentrator. Second, purely inflatable reflectors will require some make-up gas to remain inflated in space subsequently limiting the mission lifetime. Lastly, a novel approach to remove the reflector canopy, further improving the performance of the reflector, was developed and tested on the 3 m reflector. This would remove the transmission losses that would occur when collecting the solar energy and remove the need to find a canopy material that wouldn’t darken over the life of the reflector system.
AIAA Journal | 2004
Gyula Greschik; Martin Mikulas; Art Palisoc
A possible alternative to the lenticular configuration, the concept of a torus-less pressurized membrane antenna with an exact parabolic center, is introduced. For a characteristic symmetric configuration, three membrane regions are identified: the parabolic reflector center, the (wrinkled) perimeter that suspends it, and a transition zone between. Via an analysis of the pressurization kinematics, the last of the three is seen as critical. Structural economy and optimization are considered, and a design paradigm is established and demonstrated. It is also shown that there can exist mechanically sound pressurized membrane shapes for which no strain-free initial configurations correspond. The study is restricted to the pressurized membrane itself: no application-specific system integration issues are addressed.
international conference on fuel cell science engineering and technology fuelcell collocated with asme international conference on energy sustainability | 2016
Gani B. Ganapathi; Arthur Palisoc; Armin Buchroithner; Sai Nataraj; Bill Nesmith; Andrew Kindler; Gyula Greschik; Koorosh Gidanian
A low-cost rigid foam-based concentrator technology development program was funded by the DOE SunShot Initiative to meet installed cost goals of
43rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference | 2002
Gyula Greschik; Leo Lichodziejewski; Gordon Veal
75/m^2 vs. current costs of ∼
international conference on fuel cell science engineering and technology fuelcell collocated with asme international conference on energy sustainability | 2014
Gani B. Ganapathi; Art Palisoc; Bill Nesmith; Gyula Greschik; Koorosh Gidanian; Andrew Kindler
200–250/m^2. Phase 1 of the project focused on design trades and cost analyses leading to a cost-optimized self-powered autonomous tracking heliostat concept with a mirror surface area in the 100m^2 range. In Phase 2 30-year accelerated testing of the mirror modules based on ReflecTec film with 94% specular reflectivity bonded on composite foam substrate were initiated and completed in Phase 3. The tests with 15 coupons showed optical performance degradation of less than 5% in specular reflectance following 30-year equivalent UV testing and other abuse testing such as acid rain, bird dropping, thermal cycling, etc. A small scale prototype (3m×2m) heliostat design based on modular truss elements with removable mirror modules was developed in detail. In this phase components such as the dual-axis actuators were sized and selected based on wind load requirements and pointing accuracy demands were completed. Finite Element analyses for the mechanical structure with mirror modules were performed using three separate commercial codes — ANSYS, COMSOL and SolidWorks to validate the optical errors induced by wind loads on the structure up to 35 mph. Results indicated that the RMS deflections contributed to less than 0.4 mrad pointing error. Dynamic response of the heliostat indicated that the first 5 eigenmodes were in the 17–20 Hz range. The individual structure elements such as the trusses and c-rails were fabricated locally and assembled with the mirror facets in the lab for initial fit check and testing. The nine mirror facet surface errors were characterized using photogrammetry and verified using Reverse Hartmann techniques and showed to be in the order of 1 mrad or less. A three-level controller (main, gateway and heliostat) was architected and built. Tracking of the sun is done using NREL’s Sun Tracking Algorithm implemented in the gateway controller. Target-pointing vectors are calculated for each heliostat and conveyed wirelessly to the individual heliostat controllers for actuating the azimuth and elevation motors. The power subsystem consisting of solar panels and a battery provide 24V for the actuators and controller boards. The system was sized to provide adequate power for a period of 5hrs of operation when power is not available. Initial calibration will be performed with on-site camera tracking the sun’s image on a target located approximately 52m from the heliostat. Testing of the heliostat pointing under calm and windy conditions will be done to demonstrate overall performance that meet DOE targets of 4 mrad under 27 mph winds. Commercialization efforts are underway to transition the design to the commercial sector. The project is well on its way to approaching overall cost targets and current estimates are approximately S90–110/m^2 and lower costs can be achieved with alternates to the film we have identified.
44th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference | 2003
Gyula Greschik; Thomas Murphey; Martin Mikulas; W. Belvin
An attractive and straightforward means to improve the deployment characteristics and the performance of aluminum-rigidized tubes is hoop reinforcement via chord (filament) wound onto the tube. This wrap, among other advantages, (a) may prevent the unduly domination of aluminum laminate plastification during rigidization by the hoop stresses and (b) may continue to stiffen the tube wall after rigidization for improved structural performance. While the advantages of the filament wrap during the rigidization are obvious and easily demonstrable, its contribution to the performance of the deployed strut are not well understood. One of the many details on which this contribution critically depends, the elasto-plastic interaction between the aluminum laminate wall and the reinforcing wrap, is in the focus of the present paper. In particular, it is shown via a simple model that this interaction plays a critical role in defining whether the wrap can directly contribute to the deployed performance at all. A counter-intuitive conclusion of the study is that an unduly high filament stiffness can effectively eliminate any direct reinforcing effect of the rigidized tube by the wrap if certain additional conditions apply. This work complements a paper by Lichodziejewski et al. which summarizes practical and experimental aspects of the technology 1 .
Archive | 2013
Gani B. Ganapathi; Art Palisoc; Gyula Greschik; Koorosh Gidanian; Bill Nesmith; Andrew Kindler
A low-cost rigid foam-based concentrator technology development program was funded by the DOE SunShot Initiative to meet installed cost goals of
Archive | 2015
Gyula Greschik; Arthur Palisoc
75/m2 vs. current costs of